> On Mar 23, 2016, at 10:36 PM, Chris Lattner <[email protected]> wrote:
> I understand that Jordan withdrew his objection later (because no overload is
> required) but it still isn't clear to me that autoreleasepool should return a
> value.
>
> Here’s my thought process: autoreleasepool is *intentionally* looking like a
> statement, not an expression. Someday I hope it will be possible to
> break/continue/return/throw out of a closure, and at that point, it will look
> exactly like a statement.
>
> The problem with adding a return value for this is that (so far) we don’t
> allow the same thing to ‘do’, ‘if’, ‘switch’ and other statements. I’d argue
> that autoreleasepool should follow as close as possible in do’s footsteps:
> if/when we decide to expressionize these statements, at that point should we
> expressionize autoreleasepool to match.
If this is the plan, then I’d agree that adding a return value would not be
good since it would make that “inlining” more of a breaking change. But, to
some extent that ship has already sailed:
func f() {
autoreleasepool {
if (somethingWithLotsOfAutoreleasedObjects()) {
return;
}
somethingImportant()
}
}
If `autoreleasepool` is turned into a statement instead of a function, the
meaning of existing code will silently change in possibly disastrous and hard
to detect ways. Is there a plan in place to deal with this? The only idea that
occurs to me would be to leave `autoreleasepool` as is for a transitional time,
deprecated, and add a statement with a new name. Though, if a newly named
statement were to be added, then we’re back to being able to leave
`autoreleasepool` as a function with a return value and error =)
With the `rethrow`/`throws` annotation, the migration would be easier since the
compiler would catch `try autorelease {...}` as invalid and the extra `try`
could be removed.
Either way, I’m most interested in the `rethrow`/`throws` annotations since
passing a value and error back out are most error-prone part, and since it
isn’t possible to add in a wrapper. The return value would be possible to
re-add in a wrapper, of course.
-tim
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